too, also, either用法

1. too 和also用法，用于肯定句。too用于句末，also常用于句中。

e.g. I can play the piano well, and I can also play the violin although I can't play it very well. 

Tom is friendly to us. Jerry is also friendly to everyone. 

She is good at math, and she does well in Chinese, too. 

2. either用于否定句末，表示“也不”之意。

He doesn't ride to school, and I don't ride to school, either. 

He can't swim, and he can't dive, either. 

3. either 还表示“二者之一”的意思。

Would you like some tea or coffee? （您想要茶还是咖啡？）

Either is OK. (都行。)